Digital BW, The Print

The Epson hardware has very specific capability.  The jets themselves are
capable of many drop sizes but what you can take advantage of during a
single print is limited.  Take the x800 printers for instance.  The approximate
drop sizes possible are (in picoliters) about 4, 8, 20, 40, and 80.  Before starting
a page you must pick the resolution and the drop sizes to be used -- it cannot
be change during an entire page.   With variable dot you have a set of three sizes
say (4,8,20)  or  (8,20,40)  or (20,40,80).   The ultra micro dot lets you use just (4).
All inks use the same sizes and everything on the page must use the same set.

The dpi doesn't select the droplet size but does determine what has to be used.
With 2880x1440dpi there are up to 2880x1440 drops/sq.in.  and it turns out that 
4 pl drops gives enough ink to make a full black.  So you use the ultra micro,
single dot size drops.  For 1440x720 that are 1/4 the number of possible drops so 
you must use larger drops.  The only thing that makes sense is to use (4,8,20).  That
way the largest drops can be used for dMax and the smallest can be used in the
lighter areas and of course the mid size in the middle range.  Note that the smallest
dot is the same for both cases -- so the light grays will be similar in dots/sq.in.
in either resolution.   This is probably why 2880dpi is not favored particularly.  It
takes 4 times as long and the results are "similar".

If you were to go to 720x720 the 20pl dot would not be large enough 
for a dMax black so you would need to use (8,20,40) and the lightest
gray areas would show half as many bigger dots as the above cases.

So based on the dpi you pick, you must pick a large drop that is big enough to
give a dMax black.  If it turns out there are smaller dots that can be used together
with that large dot in a variable dot mode then it make sense to use it.

it just seems to me that what needs to be used is pre-determined.  In fact the
Epson manuals show all this in their table of recommended usage.

Roy

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Tom Baker 
<tbaker1328@...> wrote:
>
> As far as I can determine, the droplet size is not set by DPI.  Colorbyte says (if I 
recall correctly) that at 2880 on the x800 printers, the droplet size is limited to a 
single size per line.  At 1440 the droplet size can be differents sizes on the same line.  
They don't seem to be much in favor of 2880 profiles, apparently for this reason.  
This implies that they are using some internal software to help determine which to 
use.  If they are doing it, other RIP makers could certainly do it.
>    
>   Tom Baker
> 
> hogarth@... wrote:
>   Well, I didn't understand how the printer actually wants to work - that 
> is, given a printer resolution, a particular dot size is used by all 
> channels. Smallest dots for 2880, bigger dots for lower resolutions. I 
> thought Epson meant to use this feature for more than just that.
> 
> What I was envisioning (be careful there!) was a driver smart enough to 
> use all the dot sizes all the time, and smart enough to determine when a 
> given dot size was appropriate. The drivers (Epson, StudioPrint, QTR, 
> etc.) seem to be smart enough to run dither patterns and decide how to 
> place dots, and which dots to place, to make good smooth tonal 
> transitions. I just thought they could do this with dot sizes too, 
> because clearly variable dot size has the potential to improve the 
> smoothness of tonal transitions, and improve sharpness too. Yet variable 
> dot size doesn't appear to be used that way. My bad.
> 
> I can see how it would be good to have the biggest dots in the darkest 
> regions - to ensure good coverage of the substrate so that no "paper 
> white" shows through. As in, better Dmax. This would clearly be easier 
> to do with bigger dots since they could more easily overlap if needed. I 
> can also see that the smallest dots would be most useful in the lightest 
> tones because there you have to have some paper white showing through to 
> get those 1% tones.
> 
> But I can also see how the ink and coating are going to have a major 
> influence on when and where you need to use the big or small dots. Dot 
> gain comes to mind. If you have a lot of dot gain, you probably don't 
> need the biggest dots to ensure full coverage of the darkest areas. If 
> you have less dot gain, you might need the bigger dots. That sort of thing.
> 
> It's almost like we need to extend the ICC profiles - to carry 
> information like that to help the driver do a good job of picking dot 
> sizes as required to get the tonal transitions we want. Before that 
> though I want the ICC profiles extended to do a better job of handling 
> neutral tones ;-)
> --
> Bruce Watson
> 
> 
> 
> Tyler Boley wrote:
> 
> > --- In DigitalBlackandWhiteThePrint@yahoogroups.com, hogarth@ wrote:
> > >
> > > So... v12 doesn't have a working algorithm to pick which size dot to
> > use
> > > for each ink then? I would have thought that this is part of what you
> > > pay the big bucks for. This information doesn't make me want to lay out
> > > the money for the upgrade.
> >
> > Bruce, I'm not absolutely positive I understand what you mean by such
> > an algorithm but if I do, I think it would be extraordinarily complex.
> > It would be dependant on the nature of the particular ink, and the
> > particular media. There is obvioulsy a built in algorithm that
> > transitions from one dot size to the next, probably based on Epsons
> > own. You can control which dot size or sizes to use and how much of
> > each, per ink. But after playing with this a bit, I can't imagine how
> > it could be automated. Too many things have to be seen to decide how
> > to proceed, and for mono inks, I'm seeing no need for the larger dot
> > sizes at all in the light inks. In fact some media won't handle it.
> > I recall a thread some time ago, Roy and a few others were talking
> > about the difficulty of partitioning and linearizing multiple K inks
> > along with variable dot. I think that's one reason the K7s are best
> > used with a 2880 set up. It's only one dot size, the smallest, making
> > so many inks easier to deal with. Also, with so many inks dithering in
> > and out, I don't see why one would even need variable dot.
> > For those less masochistic than I, the standard setup without variable
> > dots works very well, as you know, and the old versions do that just
> > fine. One step beyond that in v12 would be to set the K to open to the
> > large dot size, and maybe the lightest ink start with the smallest,
> > and gain some advantage there from the new feature. Other than
> > relinearizing, not much tweaking there.
> >
> > > Any idea how your tweaked quad output would compare to non-tweaked hex-
> > > or sep-tone output in terms of print quality? In other words, if I have
> > > a hex-tone set available, should I use that rather than going through
> > > the pain and effort of tweaking the RIP for quads?
> >
> > Though I have buried my nose in some K7 output and am very impressed,
> > I have none here now for direct comparison. I don't intend to switch
> > to it so having it around taunting me would not be healthy.
> > I can say this is a step up for quads, subtle though. I sent the
> > tweaked dot setup to a very experienced pro friend, and he said he
> > made the best quad print he's ever made with it. Would most people see
> > that difference, or place a value on it? I think there is no beating
> > K7 output for neutral smooth B&W artifact free digital printing on art
> > papers that I have seen. I would not expect v12 quads with tweaked
> > dots to hold up to K7 under a loup. Without a loup, I don't know. I
> > need variable hues, so other considerations come to play.
> > I needed v12 for 9800 color, so had to get it anyway. Basically, I'm
> > reporting on miniscul obscure issues of interest to me. I hope it
> > didn't sound like an ad for the new version.
> > Both Roy and John Dean have working K6 setups right now, I think they
> > could say more about that quality.
> > Too bad we are all so far aprt, bringing everyone together with their
> > print and problems would be very informative.
> > Tyler
> 
> 
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